assume cs:code
code segment
start:
	mov ah,0
	int 16h

	mov ah,1
	cmp al,'r'
	je red
	cmp al,'g'
	je green
	cmp al,'b'
	je blue
	jmp short sret

red:
	shl ah,1
green:
	shl ah,1
blue:
	mov bx,0b800h
	mov es,bx
	mov bx,1
	mov cx,2000
    s:	and byte ptr es:[bx],11111000b
	or es:[bx],ah
	add bx,2
	loop s
sret:
	mov ax,4c00h
	int 21h
code ends
end start
